Semiconductor technologies often form extremely clean microstructure surfaces on microelectromechanical devices (often referred to as “MEMS devices”). Undesirably, extremely clean microstructure surfaces often stick together if they come into contact. When the surfaces remain stuck together, the device often is inoperable. This concept of surface sticking is known in the art as “stiction.”
A number of different factors can contribute to stiction. For example, among other things, stiction may occur during wet release of a movable MEMS microstructure, where the surface tension of a draining rinse liquid can draw the microstructure into contact with an adjacent part such as an underlying substrate (sometimes referred to as “release stiction”). Stiction also may occur when the device is in use, for example, when parts intentionally or accidentally come into contact with one another (sometimes referred to as “in-use stiction”). Stiction can be caused, for example, by capillary, electrostatic and van der Waals forces as well as by “chemical” forces such as hydrogen bonding and solid bridging. In some cases, stiction can be mitigated to some degree by coating the relevant MEMS parts with an anti-stiction material, although stiction may still occur.
Accordingly, prior to distribution of a MEMS device, MEMS device manufacturers often perform a variety of tests to determine the potential for stiction problems. Many currently available MEMS device stiction tests, however, have significant limitations. For example, some known stiction tests (which, of course, are not used during actual use of the MEMS device) in fact cause the stiction problem. Consequently, in addition to destroying the MEMS device, such tests do not accurately determine if a stiction problem actually exists. Other tests are not usable with certain types of MEMS devices. For example, some stiction tests are not usable with MEMS devices having springs with a high spring constant.